The code is a string of JS code. The sandbox contains objects which are
going to be accessible in the JS code.
It returns the last evaluated piece of JS code in code, if no timeout is
given. Otherwise, after at most timeout milliseconds, the callback gives that
result as a parameter: function(error, result) {…}.

Node example:

var localeval =require('localeval');

localeval('console.log("Do I have access to the console?")');// Throws.